Corrosion inhibitors for lubricating oils



Patented Apr. 20, 1954 UNITED STATE ATENT OFFICE CORROSION'INHIBITORSFOR LUBRICATIN G IOILS corporation of Maine No Drawing.

Application April 9, 1952,

Serial No. 281,457

8 Claims.

This invention relates to additives for lubricants and more particularlyto corrosion inhibitors of use in lubricating oils of the crankcasetype. Although the additives of the present invention are highlydesirable for use in the crankcases of passenger automobiles or similarvehicles, they are especially valuable for heavy duty service in truck,bus, aeroplane, marine and diesel engines which operate for long periodsof time at high temperatures.

With the advent of greater horsepower output in internal combustionengines and their operation at higher speeds, it became necessary to generally strengthen or stiffen the engines to withstand the increasedstresses which are cre" ated in the operating parts thereof, such as,for example, in the crankshaft or other rotating or moving parts. Newhard-metal alloy bearings such as cadmium-silver, copper-lead,nickel-cadmium, and the like, have been introduced in the automotiveindustry to replace the softer babbit metal bearings in an effort tobrace these operating parts against distortion due to the greaterforces. These hard alloy bearings exhibit superior strengthcharacteristics and are generally more satisfactory than theirpredecessor babbit metal bearings but have shown a greatersusceptibility toward the corrosive action of the acidic materialsdeveloped in the lubricating oils due to oxidation or decompositionduring use. As a consequence, efforts have been made to prevent thistype of corrosion of the newer type of bearings by the use of corrosioninhibitors in the oil and such has become an important factor in thecare and preservation of internal combustion engines.

How these corrosion inhibitors actually function in a composition ascomplex as the mixture of hydrocarbons found in lubricating oils andunder the varying conditions which exist in an operating internalcombustion engine is not precisely or positively known. However, it isbelieved that these inhibitors either prevent the corrosive substancesfrom coming into contact with' the metal surfaces'of the engine parts byforming a protective coating thereon which is impervious to thecorrosive materials and thus act as passi vators, or function, byconverting the corrosive substances in the oil into harmless,non-corrosive materials by appropriate chemical action.

Various compounds have been utilized in such corrosion inhibitingfunctions and have normally comprised metallic salts of variousphosphoric acids. Such have proved quite satisfactory in the industrybut, being metallic, are subject to some disadvantages. For example, ithas been noted that, upon the combustion of the lubrication oilscontaining these compounds, there is an objectionable ash or residueresulting from the decomposition of the lubricant. Consequently, therehas been a growing demand in some groups in the lubricating oil industryfor non-metallic additives which will not leave any ash or residue.

Furthermore, in some cases of these phosphorus-containing compounds,there has been some evidence of valve burning which has been attributedto the presence of th phosphorus.

It is therefore a principal object of the present invention to provideinhibitors for lubricating oil compositions capable of substantiallyreducing or inhibiting the corrosive effects of such lubricating oilsand/or decomposition or oxidation products thereof on metallic elements.

It is another principal object of the present invention to provide ananti-corrosive'agent which will leave no ash or residue on decompositionand which will not result in any valve burning.

We have found that the corrosive effects of the acidic materialsdeveloped in lubricating oil compositions during use may besubstantially reduced or inhibited by the addition to such compositionsof a small amount of an oil-soluble ester of cyanuric acid wherein theoxygen has been replaced by sulfur, selenium, or tellurium.

These esters may be broadly defined by the following structural formula:

inwhich X is a member of the group consisting drogen,

It is to be observed that these compounds are non-metallic and, as aconsequence, will leave no ash or residue when they are decomposed uponcombustion of the lubricating oil compositions containing them. It isfurther to be noted that these compounds do not contain any phosphorus,

as is commonly found in most anti-corrosive agents, and thus areespecially useful where phosphorus compounds have been found to causevalve burning.

The invention will be described in greater detail with particularreference to the sulfur-sub- 3 stituted esters of cyanuric acid, orthiocyanurates, but it is to be pointed out that this is not to beconstrued as limitative of the invention and that similar compoundscontaining selenium and tellurium can be substituted in order toaccomplish the objects of the present invention.

The more specific aspects of the present invention are concerned withhydrocarbon sub stituted thiocyanurates (thiocyanidines) which have beenrendered oil soluble by the attaching of hydrocarbon substituents to thesulfur atoms therein so as to be readily blendable with hydro carbonlubricating oils to form lubricating oil compositions having therequisite corrosion inhibiting properties.

As specific examples of particular compounds which have been foundsatisfactory within the principles of the present inventive concept, thefollowing compounds are cited primarily for purposes of illustration:triallyltrithiocyanurate, triethyltrithiocyanurate,tribenzyltrithiocyanurate, tributyltrithiocyanurate,dioctyltrithiocyanurate, didecyltrithiecyanurate,mono-octadecyltrithiocyanurate, tricyclohexyltrithiocyanurate, etc.

It is tobe noted, however, that the radicals selected to be attached tothe sulfur atom must be such that the resulting compound is sufficientlysoluble in lubricating oil for the purposes of the present invention andin the concentrations hereinafter set forth.

For example, Where each of R1, R2 and R3 represents an organic radical,the number of carbon atoms in each radical may be small, such astypified by the triethyl ester, without reducing the oil solubility ofthe compound below that necessary for use. Where one of the charactersR1, R2 and R3 represents hydrogen, the number of carbon atoms in the tworemaining organic radicals should be correspondingly greater, such asexemplified by the dioctyl ester. In a similar fashion, where two of thecharacters R1, R2 and R3 represent hydrogen, the number of carbon atomsin the remaining organic radical should be correspondingly even greater,such as noted in the mono-octadecyl ester. The criterion in all cases istherefore seen to be the requirement of oil solubility and the term oilsoluble or similar phrase, as used herein, limits the scope of theinvention accordingly.

Easy blending of lubricating oil additives with hydrocarbon lubricatingoils is of considerable importance from a practical and commercialviewpoint and, accordingly, while certain of the lower carbon atomradicals having decreased oil solubility characteristics can be blendedwith lubricating oils by the employment of special techniques, thedifficulty and additional expense of doing so does not warrant theirindustrial use. It is also customary in the art to prepare, ship andstore these additives in the form. of about 50% solutions in lubricatingoil, for example, so that the blender need only pour the additivecompound into the lubricating oil with suitable stirring. Additives ofdifficult solubility cannot be employed in such facile manner andconsequently are not as desirable.

The amount of the inhibitor to be mixed with the hydrocarbon lubricatingoil or other lubricant will depend to a large extent upon the nature andcharacteristics of the lubricating oil, itself; upon the particularester used; upon factors of expense and intended use of the lubricatingcomposition; upon the presence of other additives; etc. Oils having amarked tendency to oxidize or corrode metals will naturally requirelarger amounts of the additive and, conversely, oils having a lessertendency to oxidize or corrode metals will not require so much of theadditive. In general, we have found that an effective concentrationrange, which is hereinafter sometimes referred to as stabilizingamounts, may comprise from about 0.1 percent :by weight to about 5.0percent by weight of the lubricating oil. For most oils we have foundthat concentrations of from about 0.5 percent !by weight to about 2.0percent by weight of the lubricating oil have proved satisfactory.

If desired or necessary, the inhibitors of the present invention may beused in conjunction with other lubricating oil additives, for example,detergents or dispersants such as metal salts of organic acids, or pourpoint depressants such as wax naphthalene condensation products, orviscosity index improvers such as high molecular weight resins, orextreme pressure agents such as phosphorous or sulfur containing organiccompounds, and the like.

The invention will be further illustrated in greater detail by thefollowing specific examples and test results. It should be understood,however that although these examples may describe in particular detailsome of the more specific features of the inventive concept, they aregiven primarily for purposes of illustration and the invention in itsbroader aspects is not to be construed as limited thereto.

Example 1 grams of allyl chloride was slowly added to 66 grams oftrithiocyanuric acid and 74 grams of potassium hydroxide in a mixture of300 grams of ethanol and 225 grams of water at room temperature. Thereaction mixture was agitated vigorously and kept at a temperature ofapproximately 40-50 C. for 40 minutes and a yield of 89 grams oftriallyltrithiocya-nurate was obtained. This was a clear, yellow, heavyoily product which was dissolved in lubricating oil and tested in anUnderwood corrosion test machine. This test comprises heatingapproximately 1500 cc. of the oil composition for 10 hours at 325 F. inan open container providing for free circulation of air, while portionsof the oil are sprayed continuously against freshly sanded bearings. Theloss of weight in milligrams per Whole bearing is calculated and themaximum permissible corrosion loss is usually on the order of 250 mgms.The particular tests listed below employed a solventrefined,Midecontinent base oil, SAE 30:

49 grams of potassium hydroxide in 200 ml. ethyl valcohol was added atroom temperature to a slurry of 44 grams of trithiocyanuric acid. cc. ofwater was then added to give a clear twophased liquid. Then, 77 grams ofallyl chloride was added slowly from a dropping funnel with vigorousagitation. The reaction mixture was cooled in an ice water bath and thetemperature kept at about 40 C. After the addition of the allylchloride, the precipitated potassium chloride was filtered off. Theproduct was stripped up to 170 C. bath temperature with the pressurereduced to 30 mm. The clear yellow residual liquid which was obtainedweighed 58 grams, which corresponded to a yield of 78.4%. The productwas very soluble in oil and, when added to a lubricating oil and used inthe crankcase of an internal combusion engine, proved to be an excellentcorrosion inhibitor.

An Underwood test was run at l additive and the bearing weight loss perwhole bearing for cadmium-silver bearings was 7 mg., and for copper-leadbearings, it was 12 mg. (See Example 1.)

Example 3 108 grams of benzyl chloride was added slowly dropwise to amixture of 44 grams of trithiocyanuric acid and 42 grams of potassiumhydroxide in 600 cc. of alcohol at room temperature with vigorousagitation. After the addition of the benzyl chloride, the oil bathtemperature was raised to 100 C. and held at that temperature forapproximately 30 minutes. The potassium chloride which precipitated outwas filtered off. The filtrate was a clear yellow solution when hot. Oncooling, the tribenzyltrithiocyanurate crystallized out in long whiteneedles. The yield was 109 grams and was calculated to be 78.4%. Themelting point of the compound was 76-79 C.

Underwood test results at 1% additive on copper-lead bearings indicated11 mgms. loss per whole bearing.

Example 4 A solution of 105 grams of cyanuric chloride in 250 grams ofdioxane was treated with a solution of sodium ethyl mercaptide (from 62grams of ethyl mercaptan and 41 grams of sodium hydroxide at atemperature of 35 C.) over a twohour period. The reaction mixture wasagitated for an hour further and was then filtered. The dioxane wasstripped off over a water bath at 45 C. with a reduced pressure of 35mm. The residual liquid still contained some unreacted cyanuric chloridewhich was filtered off. The filtrate was heated at 100 C. for 1; houruntil no more cyanuric chloride sublimed. The product was then distilledunder vacuum. It was thiethyltrithiocyanurate and boiled at 150l52 C. at0.7 to 0.8 mm. The freezing point was found to be22.5-23 C. The yieldwas 162 grams which indicated a percent yield of 61%.

Underwood test results with 0.5% of additive indicated 69 mg. bearingweight loss per whole bearing for cadmium-silver bearings and 22 mg.weight loss per whole bearing for copper-lead bearings. The product wasoil soluble and was an excellent corrosion inhibitor when added to acrankcase lubricating oil.

Example 5 205 grams of cyanuric chloride was reacted with 124 grams ofethyl mercaptan and 81 grams of sodium hydroxide at a temperature of 40C. for 60 minutes to yield 162 grams of triethyltrithiocyanurate. Thiscorresponded to 62% yield. The heavy oily product was dissolved in asolvent refined Mid-Continent base stock lubricating oil SAE 30 andtested in an Underwood corrosion test following the procedures set forthin Ex- Although we have described but a few specific examples of ourinventive concept, we consider the same not to be limited to thespecific substances mentioned therein but to include various othercompounds of equivalent constitution as set forth in the claims appendedhereto. It is understood that any suitable changes, variations andmodifications may be made without departing from the spirit and scope ofthe invention.

What We claim is:

1. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lubricating oil having dissolved therein arelatively small amount, sufilcient to reduce the corrosive effect ofsaid composition on metallic elements of an oil-soluble compound havingthe following structural formula:

in which each of R1, R2 and R3 is a member of the group consisting ofalkyl radicals having from 1 to 18 carbon atoms, allyl, aryl andcycloalkyl radicals and hydrogen.

2. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lubricating oil having dissolved thereinfrom about 0.1% by weight to about 5.0% by weight of an oil-solublecorrosion inhibitor having the following structural formula:

in which each of R1, R2 and R3 is a member of the group consisting ofalkyl radicals having from 1 to 18 carbon atoms, allyl, aryl andcycloalkyl radicals and hydrogen.

3. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lubricating oil having dissolved thereintriallyltrithiocyanurate in an amount sufficient to reduce the corrosiveeffect of said composition on metallic elements.

4. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lubricating oil having dissolved thereinfrom about 0.1% by weight to about 5.0% by weight oftriallyltrithiocyanurate as a corrosion inhibitor.

5. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lubricating oil having dissolved thereintriethyltrithiocyanurate in an amount suflicient to reduce the corrosiveeffect of said composition on metallic elements.

6. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lu- 7 bricatingoil having dissolved thereinfrom about 0.1% by weight to about 5.0% by Weight oftriethyltrithiooyanurate as a. corrosion inhibitor.

7. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lubricating oil having dissolved thereintribenzyltrithiocyanurate in an amount sufllcient to reduce thecorrosive effective of said composition on metallic elements.

8. A hydrocarbon oil composition comprising a relatively largeproportion of a hydrocarbon lubricating oil having dissolved thereinfrom about 0.1% by Weight to about 5.0% by weight oftribenzyltrithiocyanurate as a corrosion inhibitor.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,160,293 Shoemaker May 30, 1939 2,375,733 Kaiser May 8, 1945

1. A HYDROCARBON OIL COMPOSITION COMPRISING A RELATIVELY LARGEPROPORTION OF A HYDROCARBON LUBRICATING OIL HAVING DISSOLVED THEREIN ARELATIVELY SMALL AMOUNT, SUFFICIENT TO REDUCE THE CORROSIVE EFFECT OFSAID COMPOSITION ON METALLIC ELEMENTS OF AN OIL-SOLUBLE COMPOUND HAVINGTHE FOLLOWING STRUCTURAL FORMULA: